The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Emissions control is an important factor in engine design and engine control. Nitrogen oxide (NOx) is a known by-product of combustion. NOx is created by nitrogen and oxygen molecules present in engine intake air disassociating in the high temperatures of combustion. Rates of NOx creation include known relationships to the combustion process, for example, with higher rates of NOx creation being associated with higher combustion temperatures and longer exposure of air molecules to the higher temperatures. Additionally, carbon monoxide (CO) and unburnt hydrocarbons or particulate matter (PM), frequently occurring in the form of soot or diesel/gasoline particulates, are also by-products of combustion. Reduction and management of such emissions in an exhaust aftertreatment system are desirable.
A number of strategies are known to manage emissions in an aftertreatment system. A TWC, used in conjunction with a gasoline powered engine, is known to provide within a certain temperature range a means to chemically react in real-time components within the exhaust gas flow, changing pollutants into non-polluting substances. For example, NOx is converted into nitrogen and oxygen molecules, CO is combined with oxygen to form CO2, and unburnt hydrocarbons are reformed into CO2 and water. Similarly, a diesel oxidation catalyst (DOC) in real time provides a means to oxidize CO and unburnt hydrocarbons into CO2 and water within an exhaust gas flow from a diesel engine. Lean NOx trap devices are known, utilizing a catalyst element to store or adsorb NOx, particularly during periods when the engine is operated lean of stoichiometry. The NOx trap eventually becomes full, and a cleaning or regeneration cycle must be initiated to purge the NOx trap. Regeneration cycles are known to consist of periods of stoichiometric or, preferably, rich engine operation, with reductant species (CO or unburned hydrocarbons) generated from the rich engine operation, converting the NOx into nitrogen and oxygen, as described above. Similarly, a particulate filter device (PF) stores soot from the exhaust gas stream that is generated from the engine. As the PF becomes full, a regeneration cycle must be initiated to purge the stored soot by elevating the temperature of the PF to a range conducive to oxidizing the soot. As is also known in the art, the storage capacity of devices such as the NOx trap and the PF are temperature dependent. A selective catalyst reduction device (SCR) is known to utilize ammonia as a reducing agent to facilitate the conversion of NOx. Ammonia may be introduced by the injection of urea into the exhaust gas flow from a storage tank. Additionally, oxygen can be introduced by an induction system into an oxygen depleted exhaust gas flow, facilitating the conversion of CO. Additionally, ammonia is known to be a normal by-product of reactions within a LNT or TWC under certain conditions, and processes are known to be utilized to capture or store this ammonia for later use in an SCR. However, these aftertreatment devices and the chemical reactions enabled within are temperature dependent, and if exhaust temperatures vary from the operative temperature ranges of the device, the named reactions cannot take place in real-time.
Devices trapping or storing combustion by-products provide a means to accomplish both fuel efficient operation and low emissions by periodically cleaning the storage device. As described above, a regeneration cycle typically involves operation of the device in a temperature range higher than the exhaust gas temperatures during lean operation or operation at low engine speeds and loads. If operating conditions force a suspension of a regeneration cycle, the regeneration cycle may be forced to divide into several sub-regenerations because of the interruption. Each time a sub-regeneration is initiated, the device being regenerated requires a re-heating time, requiring an additional expenditure of fuel required to heat the device. Additionally, sub-regenerations cause thermal-fatigue and shorten catalyst life. A result of partial regenerations can be sintering of the catalyst, resulting in decreased performance of the device and higher maintenance requirements.
Additional strategies are known for treating combustion by-products in an exhaust gas flow when conditions are outside of temperature ranges conducive to efficient operation of aforementioned aftertreatment devices. Strategies are known to control the temperature of an exhaust gas flow to bring either over-temperature or under-temperature exhaust gases into a temperature range more conducive to aftertreatment. For example, an air induction system can be used to introduce ambient temperature air into the exhaust gas flow, thereby lowering the temperature of the exhaust gas flow. Electrical heating devices or fuel-fired heating devices can be used within or upstream of a device to elevate the temperatures of the exhaust gas flow within the device.
Strategies are also known to protect temperature sensitive devices from high exhaust gas temperatures. For example, a TWC is frequently located in close proximity to the exhaust manifold, exposing the device to the exhaust gas flow immediately after the flow exits the engine. The catalytic element and related chemicals or coatings utilized to facilitate the reactions within the device can breakdown as a result of exposure to high temperatures. An exhaust diverter valve is known to channel some portion or all of the exhaust gas flow away from the sensitive device, thereby protecting the device from the high temperature flow.
Engine or powertrain control strategies can be implemented to modify exhaust gas temperatures being generated by the combustion cycle. As aforementioned, lean combustion modes are known to result in lower exhaust gas temperatures, and stoichiometric or rich combustion modes are known to result in higher exhaust gas temperatures. If a particular temperature range of exhaust gas is needed, an engine control strategy, as implemented for example within an engine control module, can be modified to generate the desired exhaust gas temperature. For instance, as described above in relation to regeneration cycles, a rich combustion mode can be implemented to raise exhaust gas temperatures. Alternatively, lean combustion modes can be utilized to lower exhaust gas temperatures under conditions where lean operation is possible. Also, hybrid powertrains utilizing alternative energy sources are known, such as electric machines powered by electrical energy stored in an electric storage device such as a battery. Operation of such an exemplary powertrain can include operation solely under power of an engine, solely under power of an electric machine or machines, or some combination of the two. Work output of an engine has a direct impact upon the heat carried from the engine within the exhaust gas flow. Higher engine loads require a greater throttle setting to accomplish the same engine speed. Additionally, lean combustion modes, described above, only operate under lower engine loads. Higher engine loads can require stoichiometric or rich engine modes, generating higher exhaust gas temperatures. Because the variable operation of the engine changes the resulting load upon the engine, and because the load upon the engine directly impacts the temperature of the exhaust gas flow, a hybrid control strategy can be used to modulate the engine load, and thereby modulate the resulting exhaust gas flow temperatures. For example, in periods where a lower exhaust gas temperature is required, a hybrid control strategy can control a greater amount of the load to be carried by the electric machine, lowering the load carried by the engine. Alternatively, in a period where a PF is in the process of being regenerated, a hybrid control strategy can be implemented to either transfer load to the engine by disabling or disengaging the electric machine or even increasing the load upon the engine by operating the electric machine in a generator mode, thereby increasing the load upon the engine in excess of the load normally applied to the engine.
Known powertrain architectures utilizing hybrid energy sources include torque-generative devices, including internal combustion engines and electric machines, which transmit torque through a transmission device to an output member. One exemplary powertrain includes a two-mode, compound-split, electro-mechanical transmission which utilizes an input member for receiving motive torque from a prime mover power source, preferably an internal combustion engine, and an output member. The output member can be operatively connected to a driveline for a motor vehicle for transmitting tractive torque thereto. Electric machines, operative as motors or generators, generate a torque input to the transmission, independently of a torque input from the internal combustion engine. The electric machines may transform vehicle kinetic energy, transmitted through the vehicle driveline, to electrical energy that is storable in an electrical energy storage device. A control system monitors various inputs from the vehicle and the operator and provides operational control of the powertrain, including controlling transmission operating state and gear shifting, controlling the torque-generative devices, and regulating the electrical power interchange among the electrical energy storage device and the electric machines to manage outputs of the transmission, including torque and rotational speed. Strategies for balancing the different highly efficient operation under electrical power and high output operation under combustion are known, and these balancing strategies allow for flexibility through different operating conditions. Through modulation of the various components of the powertrain, the vehicle can take advantage of operating conditions especially beneficial to particular modes of operation, reclaim kinetic energy as potential energy, and store that potential energy in an energy storage device, thereby allowing storage and later low or zero emission use of energy that would normally be dissipated through vehicle braking.
Engine control strategies utilized to enhance vehicle performance take many forms. New engine mechanisms provide means to increase efficiency. For example, cylinder deactivation is a method known in the art wherein a vehicle control system determines a required torque input from the engine, and only utilizes the proportion of cylinders in the engine necessary to efficiently deliver that torque. Another example includes enhanced engine valve operation, for instance, variable valve trains, enabling unthrottled operation controlling air intake by the opening of the valves, thereby reducing pumping losses associated with throttled operation. In another instance, variable valve trains in combination with variable spark timing and enabling engine control mechanisms allow manipulation of the combustion cycle to match optimal combustion for particular operating conditions. Variable valve trains, injection, and spark timings are known to be utilized to manipulate exhaust gas flow temperatures. For example, spark timing retarded from usual timing is known to be used to force more heat of combustion through the exhaust, thereby elevating temperatures in aftertreatment devices. Advancing, retarding, or multiple event fuel injection timing is also known to produce a similar result. Additionally, fuel injection is known to be utilized in the exhaust system or aftertreatment system to reform the fuel in the exhaust gas flow as a means to raise temperature in the aftertreatment system. Additionally, advanced engines include a variety of control strategies, for example, taking advantage of in-cylinder pressure sensing and high speed processing to optimize and adjust combustion from cycle to cycle. Additionally, new combustion processes provide flexible combustion parameters with different optimal ranges. Combustion within conventional gasoline and diesel engines was long performed at stoichiometric and lean fuel air ratio, respectively, providing a mixture of the two chemical components (fuel and oxidizer) necessary to sustain optimal combustion reaction. Modern combustion processes have been developed, for example, homogeneous charge compression ignition (HCCI), pre-mixed charge compression ignition (PCCI) and stratified charge spark ignition direct-injection (stratified SIDI), by taking advantage of unconventional charge concentrations, charge mixtures, and ignition methods to more efficiently extract energy from the charge. Each of the above improvements to engine control strategies are highly dependent upon vehicle operating conditions, such as engine speed and engine load.
Each combustion process includes ranges and conditions necessary or favorable to efficient operation. For example, HCCI combustion requires an internal combustion engine designed to operate under an Otto cycle. The engine, equipped with direct in-cylinder fuel-injection, operates in a controlled auto-ignition mode under specific engine operating conditions to achieve improved engine fuel efficiency. A spark ignition system is employed to supplement the auto-ignition combustion process during specific operating conditions. An HCCI engine operating in HCCI combustion mode creates a charge mixture of combusted gases, air, and fuel in a combustion chamber, and auto-ignition is initiated simultaneously from many ignition sites within the charge mixture during a compression stroke, resulting in stable power output, high thermal efficiency and low emissions. The combustion is highly diluted and uniformly distributed throughout the charge mixture, resulting in low burnt gas temperature and NOx emissions typically substantially lower than NOx emissions of either a traditional spark ignition engine, or a traditional diesel engine.
PCCI is a known engine operating mode and is a similar engine operating mode to the aforementioned HCCI mode. One having ordinary skill in the art will appreciate that PCCI is essentially a diesel equivalent to HCCI operated in gasoline engines. Diesel engines operating in particular speed and load ranges and running in a PCCI mode can realize advantageous engine emissions result in comparison to diesel engines operating under conventional lean operation.
Stratified charge SIDI (stratified SIDI) is also a known engine combustion mode and is a means to improve engine performance under particular operating conditions. One having ordinary skill will appreciate that stratified SIDI includes, within a particular operating range, managing the concentration and pattern of fuel-air mixture around the spark plug at the spark time using direct in-cylinder gasoline injection and intentionally creating an efficient combustion event acting upon the piston, thereby increasing the engine efficiency.
Electronic means of tracking vehicle position and coordinating a position of a vehicle with geographic, road, traffic, or other information are known. Monitoring such data is known as utilizing map preview information. A known and accessible electronic means to accomplish such data acquisition includes use of global position systems (GPS) in coordination with electronic maps, digital map software using means to track the movement of the vehicle, internet-based wireless-accessible data processing, vehicle to vehicle communications, and vehicle to infrastructure communications and other remote computing resources. Information so made available include road classification, such as highway, local road, parking lot, gravel road, etc.; speed limits for various stretches of road; traffic conditions for various stretches of road, including real-time evaluations of congestion, signals sent from cooperating vehicles experiencing traffic, analysis of cellular phone patterns in other cars, predictions based upon likely rush hour traffic or sporting event traffic; road slopes; road curvature; location and status of traffic lights, signals, construction zone markers, speed bumps, or other traffic direction indicators impacting vehicular travel; existence or lack of features likely to impact travel along a certain stretch of road, such as exit ramps or truck weigh stations; and analysis of vehicle or specific operator driving patterns, habits, registered schedules, electronic planner calendars, or other predictive measures. Additionally, likely routes of travel can be estimated based upon operator entered destinations, computerized analysis of driver habits and patterns, or other means known in the art.